With the increasingly more widespread use of identity cards, cheque cards, personal code-key cards and the like it is becoming increasingly more important to safeguard such cards against abuse, forgery and deception. It is known to provide identifying cards of the kind in question with an information carrier embedded therein which contains an alpha-numerical card number in digital form. This card number is also interleafed with parts of the principal information recorded in a principal information trace. In other words, the principal information trace contains a mixed information consisting of principal information data and the card number. The card number is concealed in the principal information and difficult to isolate and identify. For checking, or verifying the card, the card number is filtered out of the principal information trace and compared with the fixed card number recorded on the accessory or secondary information carrier. The card will be accepted as genuine only if the said fixed card number agrees with the concealed card number in the principal information trace. This makes it impossible to transfer any information recorded, for example in a magnetic trace of an identity card by duplication to the information trace of another card without such deception being detected, because the cards are relatively clearly distinguished by the fixed information carriers embedded therein which show relatively different card numbers.
According to another known identification method a specifically individual information is stored unchangeably on an identifying card. When this identifying, or code-card is initially set up the permanent information present on that card is tied or linked with a secret key information and recorded on the information trace of the card. For checking the identifying code card a testing information is formed from selected parts of the permanent information and of the secret key information and this is checked for agreement with the permanent information stored on the card.
These conventional methods simply involve a process of interleafing or interweaving the information which is fixedly applied to the data carrier into the useful information. The interleafing pattern is however liable to be detected by a comparison of several cards with each other. For this reason conventional methods additionally resort to a complex technology in the production of the cards in order to prevent counterfeit right from the setting up of the data carrier.